Electrospray Printing of Polymeric and Metallic Coatings for Electronics Packaging

Polymer and metal surface coatings have many applications in electronics packaging, including electrical isolation, environmental protection, and shielding from electromagnetic interference (EMI). We report on the use of electrospray printing to deploy these materials. In electrospray printing, strong electric potentials are used to atomize a liquid precursor solution into a spray of electrically-charged droplets containing the print material. In flight the carrier solvent evaporates, leaving behind particles of solute material that aggregate to form thin, continuous, conformal films with controlled microstructures. The electrophoretic nature of electrospray printing allows for highly conformal coatings to be created on complex surface geometries, as well as non-line-of-sight surfaces. The print conditions govern the particle morphology, allowing fine control of the film microstructure, and thus, its functional characteristics. In this work, we use electrospray printing for creating conformal polymeric and metallic films. Polyimide was used to print films ranging in thickness from 100 nm up to several micrometers with sub-100 nm surface roughness. The electrospray-printed films were able to sustain breakdown field strengths of nearly 400 V/μm. Metal films were printed from silver nanoparticles in triethylene glycol monomethyl ether to provide EMI protection to system in package (SiP) architectures. The dielectric properties of the target and stencil are manipulated to allow material deposition onto insulators, such as epoxy. The relationship between the print parameters and film characteristics was established. For EMI shielding, the goal is to provide a minimum of 60 dB of isolation at a frequency of 1 GHz.